Tank drain system



July 28, 1959 R. B. UHLL ETAL 2,896,657

, TANK DRAIN SYSTEM Filed Sept. 21. 1955 WATER Fig. 1 Roy B. um Edgar J. Luefzelsc/mab INVENTORS.

United States Patent 01 TANK DRAIN SYSTEM Roy B. Uhll, Lansing, Ill., and Edgar J. Luetzelschwah,

Highland, Ind., .assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana This invention relates to storage vessels or tanks which normally contain two immiscible liquids of dififerent densities wherein it is desired to drain the lower liquid layer. More particularly the invention relates to oil storage tanks which have a water bottom and the draining away of that water bottom.

In storage tanks or vessels where a water bottom is formed, either due to rain passing into the tank or entrained water settling out, it is necessary to periodically drain away the water bottom. The simplest way of doing this has been to have a conduit or pipe passing through a tunnel beneath the tank and communicating with the interior of the tank. The water is drained away periodically by opening a valve on this drain line. In another method, the tank is provided with a shallow well in the bottom. (Merely a small depression large enough to take the wter drain pipe.) The drain pipe extends from the well up through the wall of the tank to the exterior of the tank and is provided with a valve. Inboth these systems, the water is drained either to a sewer or is dumped on the ground.

In regions where winter temperatures are low enough to freeze water, considerable difiieulty is experienced with the freezing of these lines since they contain water be tween the valve and the end inside the tank. Various methods of heating this line are used. The most economical one appears to be the use of decomposition of manure which is packed around the line in the valve. High maintenance results from this procedure because the acids from the manure corrode the line.

A more recent method of draining the tanks has been to utilize a valve which is inside the tank and is operated by an extension which passes through the wall of the tank. This type of valve is expensive because a special supply must be maintain in the stock room and maintenance is expensive since the tank must be drained in order to make repairs on the valve.

An object of the invention is a drain system for tanks or storage vessels that contain two immiscible liquids of difierent densities, which results in the formation in the tank of anupper liquid layer and a lower liquid layer, said drain system permitting withdrawal of the lower liquid layer. Another object of the invention is a drain system for tanks containing an upper oil layer and a lower water layer. Still another object is a drain system for oil storage tanks which have a water bottom, which drain system does not require protection against freezing during winter months. Yet another object is a drain system for oil storage tanks containing a water bottom, which drain system automatically expels water from the external portion of the water withdrawal conduit. A further object is a method of removing water bottoms from oil storage tanks whereby water does not remain in the water withdrawal line and thereby freezing is avoided during winter months. Other objects will become apparent in the course of the detailed description of the invention.

2,896,657 Patented July 28, 1959 ice Figure 1 of the annexed drawing shows one embodiment of the invention,

Figure 2 of the annexed drawing shows another embodiment of the invention.

The invention is described in connection with the annexed drawing which is made a portion of this specification. It is to be understood that the-figures represent only two embodiments of the invention and only one type of tank or storage vessel. Other modifications of the invention and its adaptation to other types of tanks will be readily apparent to those skilled in the art.

In Figure 1, there is illustrated an oil storage tank 11, which tank comprises a bottom portion 12 and walls 13 which are substantially perpendicular to said bottom. Bottom 12 is provided with a shallow well 14, which well consists merely of a depression in the bottom surface of the tank. It is to be understood that this tank may be an ordinary cylindrical tank with an open top or it may be a conventional cone roof tank or it may be a floating roof tank. Also, the invention may be utilized with relatively small storage tanks which are cylindrical in configuration or eliptical in configuration, such as are used extensively for supplying small heating plants.

Tank 11 is adapted to contain two immiscible liquids of different densities which form an upper liquid layer and a lower liquid layer within the tank. More specifically, the tank holds an oil such as a hydrocarbon oil or it may be a fatty oil or a vegetable oil. The lower liquid layer in this embodiment consists of water which normally results from the coalescing of water which has l been entrained in the oil prior to entry into the tank.

' The lower liquid layer (water layer or water bottoms) is withdrawn from tank 11 by way of the drain system of this invention. A first conduit 16 extends from the interior of the tank near bottom 12; herein the interior end of conduit 16 extends into well 14. Conduit 16 extends through the wall of the tank to a point outside the tank, hereinafter spoken of as beyond the exterior wall of the tank. Conduit 16 is provided with a block valve means 17. A conduit 18 extends from block valve 17 to a sewer not shown, permitting passage of the water from tank 11 to the sewer when valve 17 is open. Conduit 16 and conduit 18 are, in this embodiment, ordinary steel pipe. Valve 17 is a standard gate valve. Other types of valves may be utilized.

A second conduit 21 enters the interior of tank 11 at a point above conduit 16 where normally the upper liquid layer would be present. Simply, the conduit 21 is connected with tank interior at a point where it will be in contact with the oil when the water draining operation has been completed. Second conduit 21 is joined to first conduit 16 at a point between the valve and the exterior wall of the tank. Second conduit 21, in this embodiment, is provided with a block valve 22.

Using the embodiment set out in Figure 1, the water bottom is drained from tank 11 by an operator opening valve 17. Water flows through conduit 16, valve 17 which connects to conduit 18, and conduit 18 until the operator believes that the water layer has been reduced to a sufiicient point. It is not usual to attempt to withdraw all the water bottom. When sufficient water has been withdrawn, the operator closes valve 17 and opens valve 22. The upper liquid layer flows through conduit 21, open valve 22 and into conduit 16. Thus there is present, exposed to outside weather in conduits 21 and 16, the oil which has a freezing point very much lower that that of Water. Regardless of the temperature outside, under normal atmospheric conditions the oil in conduits 16 and '21 will remain fluid even though no insulation or other protection is given to the drain system.

In Figure 2 there is depicted another embodiment of the drain system. Tank 31, in this embodiment, comprises a bottom portion 32 provided with a shallow well 33 and sides 34. Conduit 36 extends from near the bottom of well 33 through wall 34 to valve 37. A discharge conduit 38 is provided to pass water beyond the valve to a sewer not shown. Conduit 39 connects with the interior of the tank at a point wherein the upper liquid layer is present when the water bottoms has been withdrawn to valve 37 Valve 37 is a two-way valve which permits either water to pass through conduits 36 and 38 or oil to flow through conduit 39 and conduit 36 back into the tank.

In this embodiment, the operator merely turns valve 37 to permit withdrawal of water by way of conduits 36 and 33, and when sufficient water has been withdrawn, he turns the valve to permit flow of oil through conduits 3? and 36 back into the tank, thereby forcing water out of valve 37 and conduit 36 back into the tank.

It is to be understood that other types of valves may be used; for example, a three-way valve might be used. Also, it is not necessary that the tank bottom be provided with a shallow well, as drainage can be carried out by having the water drainage conduit end at a point an inch or two above the flat bottom of the tank.

The embodiment set out in Figure 1 was installed in several large oil tanks in a petroleum refinery situated in the northern midwest. This refinery had experienced considerable maintenance trouble with corrosion of outside lines due to manure protection and also to cracking of valves during winter months due to freezing of the lines. One winters experience with .the drain system of Figure 1 showed no freezing of the lines even though no insulation was provided and no maintenance requirements due to freezing weather conditions. This very simple drain system has completely eliminated all the difficulties of the prior art systems.

Thus having described the invention, what is claimed is:

l. A liquid hydrocarbon storage tank containing a minor amount of water which forms a bottom water layer and a major amount, relative to said water present, of

liquid hydrocarbon which forms an upper hydrocarbon layer said tank being provided with drain system which,

permits withdrawing substantially all of the lower water layer, said drain system comprises a first conduit which extends upwardly from near the interior bottom of said tank and substantially horizontally through the wall of said tank to a point beyond the exterior wall of said tank the exterior end of said first conduit being below the horizontal portion thereof and the level to which said water layer is to be withdrawn, a second conduit communicating with the interior of said tank at a point normally occupied by liquid hydrocarbon and with the exterior portion of said first conduit, and valved means positioned in said second conduit and in the horizontal part of said first conduit adapted for withdrawal of water from said tank through said first conduit and termination of flow from the tank to said portion through said second conduit and alternatively for flow of liquid hydrocarbon through said second conduit and said portion of said first conduit back into said tank, said second conduit and said first conduit between the wall-of said tank and said valve means being normally full of liquid hydrocarbon thereby eliminating possible freezing of water in said first conduit.

2. The drain system of claim 1 wherein the internal portion of said first conduit extends into a shallow well positioned in the bottom of said tank.

3. The drain system of claim 1 wherein said valve means is a two-way valve.

4. The drain system of claim 1 wherein said valve means comprises a block valve positioned in the external portion of said first conduit beyond the junction of said conduits and a block valve positioned in the external portion of said second conduit.

References Cited in the file of this patent UNITED STATES PATENTS 1,161,243 Oliver Nov. 23, 1915 

